Colouring defect of a cubic graph and the conjectures of Fan-Raspaud and Fulkerson

Ján Karabáš, Edita Máčajová, Roman Nedela, Martin Škoviera

Published 2023-12-21Version 1

We introduce a new invariant of a cubic graph - its regular defect - which is defined as the smallest number of edges left uncovered by any collection of three perfect matchings that have no edge in common. This invariant is a modification of defect, an invariant introduced by Steffen (J. Graph Theory 78 (2015), 195--206), whose definition does not require the empty intersection condition. In this paper we discuss the relationship of this invariant to the well-known conjectures of Fulkerson (1971) and Fan and Raspaud (1994) and prove that defect and regular defect can be arbitrarily far apart.